The present invention relates to a disc brake having an improved torque-carrying structure which can suppress squeaks during braking.
A conventional disc brake has a pair of pads, which are to be brought into frictional contact with the brake disc, mounted between guide portions provided opposite to each other on the torque member or caliper so as to be slidable in the axial direction of the disc. The guide portions have guide grooves or protrusions in or on which the backing plates of the pads engage to unrotatably hold the pads and to carry braking force applied from the pads on their torque-carrying surfaces. The guide portion has a point at which a force reacting or counteracting the braking force applied from the pads is produced. On the conventional disk brake, this point is disposed on the line passing the center of the brake cylinder for biasing the pads and extending tangentially of the disc, or on the opposite side of the above line relative to the center of the disc.
In this arrangement, as shown in FIG. 3A, braking forces Fa and Fb that act on two points of the pads at the leading and trailing sides have Y-components Fay and Fby in opposite directions. The components Fay and Fby produce a moment M1 that tends to rotate the pads 1 counterclockwise in the figure.
Since the pads 1 are inclined counterclockwise relative to the torque member 2, a reactive force is produced at the point where the pads 1 engage the guide portion at the trailing side of the disc, i.e. point A at the outermost end of a torque-carrying surface 3a (see FIG. 3B).
On the other hand, the tangential components (or tangential forces) Fax and Fbx of the forces Fa and Fb have a center that coincides with the center of biasing force, that is, the center O of the brake brake cylinder 4. Since the point A at which the reactive force is produced is located nearer to the outer circumference of the disc than is the center O of the brake cylinder, a moment M2 is produced that tends to rotate the pads clockwise. Thus, the sum of the moments M1 and M2 acting on the pads tend to be small because they negate each other. In this prior art arrangement, the pads tend to vibrate during braking because it is impossible to restrain the movement of the pads with a sufficiently strong force.
In an arrangement in which the point A at which the reactive force is produced is on the line passing the point O and extending tangentially relative to a circle concentric with the disc, the moment M2 is not produced because the length of its moment arm is zero. Thus, only the moment M1 acts to restrict the movement of the pads, which is not sufficient to restrain them, so that it is impossible to prevent vibration of the pads.
Squeaks of a disc brake are the result of resonance of the entire brake, which occurs if the pads vibrate due to fluctuating torque resulting e.g. from stick slip. Thus, in order to prevent squeaks of a disc brake, the pads have to be mounted rigidly so that they do not vibrate.
Unexamined Japanese Utility Model Publication 56-7129 discloses a technique for producing moment in a reverse direction that is greater than the moment in the normal direction. In this arrangement, since the two moments, which are opposite in direction, negate each other, it is impossible to restrain the pads with a sufficiently strong force.
An object of the present invention is to provide a disc brake having a means for restraining the pads strongly during braking, and thereby reducing squeaking of the brake.